A greenhouse experiment was conducted to evaluate the freezing damage in some pistachio rootstocks by ion leakage and pH changes of leaked solution. A factorial experiment was carried out in randomized block designs (RBD) with three factors: Temperature (A) including 4 ̊C, 0 ̊C, -2 ̊C, -4 ̊C, -6 ̊C, Time (B) including 3, 12, 24h , and Rootstock (C) including P. vera cv 'Badami Zarand' (V13) and 'Sarakhs' (S5), P. mutica (M1)and P. atlantica (A7). For this, one-year-old seedlings were kept at these five temperatures in incubator for 2 hours. Then in the first 24 hours in three hour intervals and during four days, EC and pH in leaked solution were measured daily. After four days the seedling samples were autoclaved at temperatures 105°C for 4 minutes to destroy all cell membrane. EC and pH of remaining solution were measured again and the percentage of ionic leakage was calculated. The results showed that the best time to evaluate the pH and ionic leakage was 24 hours after incubation of samples. Based on the results, ionic leakage dramatically increased with decreasing temperatures from 0°C to -6°C, while pH of leaked solution had no significant difference in 0°C and 4°C temperature treatments. When temperature reduced from 0°C to -6°C, like ionic leakage, pH greatly reduced. So the pH of the leaked solution could be an appropriate tool to study the freezing damage of pistachio rootstocks. Based on the results of pH and ionic leakage, P. mutica and P. atlantica were the most frost tolerant and sensitive rootstocks of this experiment, respectively.
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